The present invention relates to a light beam scanning apparatus for scanning a plurality of laser beams in an image formation apparatus such as a digital copier or a laser printer which forms a single electrostatic latent image on a single photoconductor drum by simultaneously performing scanning and exposure on the photoconductor drum by using the plurality of laser beams.
In recent years, there have been developed various digital copiers according to scanning and exposure using a laser light beam (hereafter referred to as the light beam) and an electrophotographic process.
Recently, a multi-beam digital copier is developed for increasing an image formation speed. The multi-beam system generates a plurality of light beams and simultaneously scans a plurality of lines using these light beams.
Such a multi-beam digital copier is equipped with a semiconductor laser oscillator for generating a plurality of light beams and an optical unit as a light beam scanning apparatus. The optical unit chiefly comprises a rotating polygon such as a polygon mirror, a collimator lens and an f-xcex8 lens for reflecting each light beam from the plurality of laser oscillators toward a photoconductor drum and scanning on a photoconductor drum using each light beam.
Conventionally, the optical unit of the multi-beam digital copier controls scanning direction exposure positions and passage positions of light beams. The scanning direction exposure position control relates to controlling light beam positions in a horizontal scan direction. The passage position control relates to controlling light beam positions in a vertical scan direction.
An embodiment of this technology is proposed in U.S. patent application Ser. No. 9/667,317. According to the embodiment, a pair of sensors detect passage points of light beams scanning a photoconductor drum surface in the vertical scan direction in order to control light beam positions by detecting light beams with high precision in a wide range. Each of the pair of sensors is formed of a trapezoid pattern, for example. The pair of sensors are arranged at a position equivalent to the surface to be scanned and symmetrically to each other with a specified interval. A light beam scanning position is determined by a value obtained by integrating output differences from the pair of sensors.
U.S. patent application Ser. No. 9/816,773 proposes a pair of sensors comprising two sawtooth patterns for detecting a light beam. Like U.S. patent application Ser. No. 9/667,317, the proposal in Ser. No. 9/816,773 determines a light beam scanning position by using the processing circuit for integrating output differences from the pair of sensors.
However, when a light beam is defocused due to a chronological change in the optical system, etc., the light beam accuracy is degraded, disabling a correct image from being output. A similar phenomenon may occur when a light beam quantity becomes insufficient due to a chronological change, etc. In these cases, a conventional light beam scanning apparatus cannot easily detect light beam defocusing or insufficient power, causing the possibility of deteriorating the light beam accuracy and the output image quality.
Further, a complicatedly configured optical system may generate light called a flare near an irradiated light beam spot. This flare is not so serious as to affect a formed image, but may affect the light beam control. Due to the flare, the conventional light beam scanning apparatus may not be able to control the light beam to a specified position or control positioning of a plurality of light beams at a specified interval.
It is an object of the present invention to provide light beam scanning apparatus capable of controlling a light beam with high precision.
A light beam scanning apparatus according to the present invention comprises: a light emitting device which generates a light beam; a light beam scanning member which scans a light beam against a scanned surface so that the light beam output from the light emitting device scans on the scanned surface in a horizontal scan direction; a sensor which is arranged on the scanned surface or a position equivalent to a scanned surface, detects a light beam scanned by the light beam scanning member, and outputs an electric signal; a mirror which changes a passage position for a vertical scan direction of a light beam scanned by the light beam scanning member in a horizontal scan direction; a detection section which detects a maximum value for an electric signal output from the sensor in response to a light beam with its passage position gradually moved by the mirror; and a control section which determines a normal light beam when a maximum value detected by the detection section is greater than a specified reference value, and determines a defocused light beam when the maximum value is smaller than a specified reference value.
A light beam scanning apparatus according to the present invention comprises: a light emitting device which generates a light beam; a light beam scanning member which scans a light beam against a scanned surface so that the light beam output from the light emitting device scans on the scanned surface in a horizontal scan direction; a sensor which is arranged on the scanned surface or a position equivalent to a scanned surface, detects a light beam scanned by the light beam scanning member, and outputs an electric signal; a mirror which changes a passage position for a vertical scan direction of a light beam scanned by the light beam scanning member in a horizontal scan direction; a detection section which detects a maximum value for an electric signal output from the sensor in response to a light beam with its passage position gradually moved by the mirror; and light quantity detection section which detects the light beam quantity when a maximum value detected by this detection section is smaller than a specified reference value; and a control section which determines a normal light beam when a maximum value detected by the detection section is greater than a specified reference value, determines an insufficient light beam quantity when the maximum value is smaller than a specified reference value and a light beam quantity detected by the light quantity detection section is smaller than a specified reference quantity, and determines a defocused light beam when the maximum value is smaller than a specified reference value and a light beam quantity detected by the light quantity detection section satisfies a specified reference quantity.
A light beam scanning apparatus according to the present invention comprises: a light emitting device which generates a light beam; a light beam scanning member which scans a light beam against a scanned surface so that the light beam output from the light emitting device scans on the scanned surface in a horizontal scan direction; a plurality of sensors each of which is formed wider than a width in a vertical scan direction of the light beam including light generated near an irradiated spot of the light beam, is arranged on the scanned surface or a position equivalent to a scanned surface so that a fine gap is provided in the horizontal scan direction, and outputs an electric signal corresponding to an irradiated light beam quantity. A mirror which changes a passage position for a vertical scan direction of a light beam scanned by the light beam scanning member in a horizontal scan direction; and a control section which controls a light beam""s passage position by using the mirror so that a centrobaric position of the light beam quantity detected by two adjacent sensors out of the plurality of sensors matches a gap between the two sensors.
A light beam scanning apparatus according to the present invention comprises: a plurality of light emitting devices configured to output an light beam; a light beam scanning member which scans a light beam against a scanned surface so that the light beam output from the light emitting device scans on the scanned surface in a horizontal scan direction; a plurality of sensors each of which is formed wider than a width in a vertical scan direction of the light beam including light generated near an irradiated spot of the light beam, is arranged on the scanned surface or a position equivalent to a scanned surface so that a fine gap is provided in the horizontal scan direction, and outputs an electric signal corresponding to an irradiated light beam quantity; a mirror which changes a passage position for a vertical scan direction of a light beam scanned by the light beam scanning member in a horizontal scan direction; and a position detection sensor which is arranged on the scanned surface or a position equivalent to a scanned surface and continuously changes output values according to changes in scanning positions of the light beam; a control section which computes a difference between two output values, i.e., an output value from the position detection sensor when a centrobaric position for the light beam quantity matches a gap between first and second sensors adjacent to each other out of the plurality of sensors and an output value from the position detection sensor when a centrobaric position for the light beam quantity matches a gap between the second sensor and a third sensor adjacent thereto, and provides control so that an interval between light beams equals the computed difference.
A light beam scanning apparatus according to the present invention comprises: a light emitting means for outputting a light beam; a light beam scanning means for scanning a light beam output from this light emitting means onto a scanned surface in a horizontal scan direction; a detection means, arranged on the scanned surface or a position equivalent to a scanned surface, for detecting a light beam scanned by the light beam scanning means, and outputting an electric signal; a change means for changing a passage position for a vertical scan direction of a light beam scanned by the light beam scanning means in a horizontal scan direction; a detection means for detecting a maximum value for an electric signal output from the detection means in response to a light beam with its passage position gradually moved by change means; and a control means for determining a normal light beam when a maximum value detected by the detection means is greater than a specified reference value, and for determining a defocused light beam when the maximum value is smaller than a specified reference value.
A light beam scanning apparatus according to the present invention comprises: a light emitting means for outputting a light beam; a light beam scanning means for scanning a light beam output from this light emitting means onto a scanned surface in a horizontal scan direction; a detection means, arranged on the scanned surface or a position equivalent to a scanned surface, for detecting a light beam scanned by the light beam scanning means, and outputting an electric signal; a change means for changing a passage position for a vertical scan direction of a light beam scanned by the light beam scanning means in a horizontal scan direction; a detection means for detecting a maximum value for an electric signal output from the detection means in response to a light beam with its passage position gradually moved by change means; and a light quantity detection means for detecting the light beam quantity when a maximum value detected by this detection means is smaller than a specified reference value; and a control means for determining a normal light beam when a maximum value detected by the detection means is greater than a specified reference value, determining an insufficient light beam quantity when the maximum value is smaller than a specified reference value and a light beam quantity detected by the light quantity detection means is smaller than a specified reference quantity, and determining a defocused light beam when the maximum value is smaller than a specified reference value and a light beam quantity satisfies a specified reference quantity.
A light beam scanning apparatus according to the present invention comprises: a light emitting means for outputting a light beam; a light beam scanning means for scanning a light beam output from this light emitting means onto a scanned surface in a horizontal scan direction; a plurality of detection means each of which is formed wider than a width in a vertical scan direction of the light beam including light generated near an irradiated spot of the light beam, is arranged on the scanned surface or a position equivalent to a scanned surface so that a fine gap is provided in the horizontal scan direction, and outputs an electric signal corresponding to an irradiated light beam quantity; a change means for changing a passage position for a vertical scan direction of a light beam scanned by the light beam scanning means in a horizontal scan direction; and a control means for controlling a light beam""s passage position by using the change means so that a centrobaric position of the light beam quantity detected by two adjacent detection means out of the plurality of detection means matches a gap between the two detection means.
A light beam scanning method according to the present invention comprises: scanning a light beam output from a light emitting device onto a scanned surface in a horizontal scan direction; detecting a light beam scanned in a horizontal scan direction and outputting an electric signal by using a sensor which is arranged on the scanned surface or a position equivalent to a scanned surface; gradually moving a passage position for a vertical scan direction of the light beam scanned in a horizontal scan direction; detecting a maximum value for an electric signal output from the sensor in response to a light beam with its passage position gradually moved; determining a normal light beam when the detected maximum value is greater than a specified reference value; detecting the light beam quantity by using a light quantity detection section when the maximum value is smaller than a specified reference value; determining an insufficient light beam quantity when the maximum value is smaller than a specified reference value and the light beam quantity is smaller than a specified reference quantity; and determining a defocused light beam when the maximum value is smaller than a specified reference value and a light beam quantity satisfies a specified reference quantity.
A light beam scanning method according to the present invention comprises the steps of: scanning a light beam output from a light emitting device onto a scanned surface in a horizontal scan direction; detecting a light beam scanned in a horizontal scan direction and outputting an electric signal by using a sensor which is arranged on the scanned surface or a position equivalent to a scanned surface; gradually moving a passage position for a vertical scan direction of the light beam scanned in a horizontal scan direction; detecting a maximum value for an electric signal output from the sensor in response to a light beam with its passage position gradually moved; determining a normal light beam when a maximum value detected by this step is greater than a specified reference value; and determining a defocused light beam when the maximum value is smaller than a specified reference value.
A light beam scanning method according to the present invention comprises the steps of: scanning a light beam output from a light emitting device onto a scanned surface in a horizontal scan direction; detecting a light beam scanned in a horizontal scan direction and outputting an electric signal by using a sensor which is arranged on the scanned surface or a position equivalent to a scanned surface; gradually moving a passage position for a vertical scan direction of the light beam scanned in a horizontal scan direction; detecting a maximum value for an electric signal output from the sensor in response to a light beam with its passage position gradually moved; determining a normal light beam when this detected maximum value is greater than a specified reference value; detecting the light beam quantity by using a light quantity detection section when the maximum value is smaller than a specified reference value; determining an insufficient light beam quantity when the maximum value is smaller than a specified reference value and the light beam quantity is smaller than a specified reference quantity; and determining a defocused light beam when the maximum value is smaller than a specified reference value and a light beam quantity satisfies a specified reference quantity.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.